Crystal structures and magnetic properties of two- and three-dimensional malonato-bridged manganese(ii) complexes

Abstract

Two new manganese(II) compounds of formula [Mn(mal)(H₂O)(2,4′-bpy)]_n (1) and [Mn₂(mal)₂(H₂O)₂(4,4′-bpy)]_n (2) (2,4′-bpy = 2,4′-bipyridine, 4,4′-bpy = 4,4′-bipyridine and H₂mal = malonic acid) have been prepared and structurally characterized by X-ray crystallography. Their structures are made up of two- (1) and three-dimensional (2) arrangements of manganese atoms linked by carboxylate-malonate groups in the anti–syn bridging mode (1 and 2) and bis(monodentate) 4,4′-bpy (2). The 2,4′-bpy group in 1 acts as a monodentate ligand. Each manganese atom in 1 and 2 is six-coordinated with four carboxylate-oxygens in the equatorial plane and a nitrogen atom and a water molecule in the axial positions. The magnetic properties of 1 and 2 and those of the related sheet-like polymer [Mn(mal)(H₂O)₂]_n (3) (whose structure was published elsewhere, orthorhombic Pca2₁) have been investigated in the temperature range 2.0–290 K. The magnetic coupling between the manganese(II) ions in 1 and 2 through the single carboxylato bridge is weakly antiferromagnetic and practically identical (Jca. −0.2 cm⁻¹). Weak antiferromagnetic coupling is also observed in complex 3 (occurrence of carboxylate bridges in the anti–anti and anti–syn bridging modes) together with spin canting behaviour at very low temperatures (T_c = 2.7 K). The antisymmetric exchange is most likely responsible for the small canting observed in 3.